Nondestructive inspection heads for components having limited surrounding space

ABSTRACT

An inspection head where non-destructive inspection is structured to fit into narrow spaces, and to accurately and repeatably move an inspection probe along a surface to be inspected. Movement of the inspection head along an X, Y, Z, Θ, and Φ-axis is precisely controlled by individual drive mechanisms.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to non-destructive inspection of turbinecomponents. More specifically, the invention provides inspection headsfor positioning sensing elements on the surface of turbine rotor discson either a fully assembled rotor or on discs that have been removedfrom the rotor in a controlled, repeatable manner.

2. Description of the Related Art

The blades of steam turbines are attached to discs and are subjected tosignificant stress due to the heat, pressure, and vibrations withintheir operating environments. It is therefore necessary to periodicallyinspect these discs for surface cracking, internal cracking, and pittingat the blade attachment area and the rotor attachment area, known as thedisc bore. If such inspections locate indications of defects beginningto form that are not sufficient to take the disc out of service, it isdesirable to ensure that later inspections focus on locations within thediscs where the indications were found in the previous inspection.

Turbine discs are presently inspected using sensing elements such asultrasonic probes and eddy current probes, the operation of which iswell known in the art. Presently used probes are hand held, therebylimiting the positional accuracy of the inspection, and therepeatability with which the probes may be positioned.

Accordingly, there is a need for a means of accurately and repeatablypositioning an inspection probe in a desired location with respect to aturbine disc. There is an additional need for such probes to fit withinthe small space available between discs within a typical turbine rotorassembly, thereby avoiding a need to remove the discs from the turbinefor inspection.

SUMMARY OF THE INVENTION

The present invention provides a non-destructive inspection head that isparticularly useful for inspecting the discs of turbines, andparticularly the high stress areas, such as the blade attachment areaand the disc bore area (where the disc is attached to the rotor using a“shrink fit” process for steam turbines.

For purposes of this description, the X-axis is defined as an axissubstantially horizontal and substantially parallel to a disc beinginspected. The Y-axis is defined as an axis that is substantiallyvertical, and also substantially parallel to a disc being inspected. TheZ-axis is defined as an axis that is substantially horizontal, andsubstantially perpendicular to a disc being inspected. The Θ-axis isdefined by rotation about the Z-axis. Lastly, the Φ-axis is defined byrotation around the X-axis.

The invention is structured to place an inspection probe, for example,an ultrasonic probe or an eddy current probe, adjacent to or against adisc to be inspected, while the disc remains mounted to a rotor. Theturbine blades may or may not be attached to the disc during theinspection. The probe may be raised between the discs, and adjacent tothe disc to be inspected, by presently available devices. As it iscurrently designed, one probe and head assembly is positioned on eitherside of the disc to be inspected. This provides a complete inspectionwithout moving the base unit. Once the inspection head is properlypositioned, the head itself is structured for movement along at leastsome of the X axis, Y axis, Z axis, Θ-axis and Φ-axis. Movement alongeach of these axes is controlled by a separate drive mechanism, so thatthe probe may move independently along any axis, or along more than oneaxis, as necessary to properly position the probe. The Θ-drive andconsequentially the probe are free floating in a semi-spherical areaatop the Z-drive, which allows for proper contact of the face of theprobe to the disc over the various ranges of disc geometry and probecontact face contours.

If an ultrasound probe is used, a delivery/recirculation system for anultrasonic coupling medium, for example, water, may also be provided.The system is structured to dispense water between the propad and thecomponent to be expected, thereby providing effective ultrasoniccoupling between the probe and the component. A catch basin is locatedbelow the component, for catching the water so that it may berecirculated throughout the inspection process.

The inspection heads may be configured specifically to inspect specificdiscs on a turbine rotor assembly. For example, a linear drive headproviding for movement along only the X and Y axes may be utilized forinspections near the blade attachment region, where the surfaces may beinspected along a straight line, and where the Jack of Z and Θ drivemechanisms enables the inspection head to be smaller, better fittingwithin tight spaces. An arc drive head having an X axis drive and aΦ-axis drive may be utilized to inspect discs having a curved geometry.A standard head, having X-axis, Y-axis, Z-axis, and Θ-axis drives may beutilized to scan disc in the bore region, where the disc contacts therotor, and is particularly useful for inspecting regions of turbinediscs from the blade attachment area to the disc bore regions. Lastly, alow clearance head having X-axis, Y-axis, Z-axis, and Θ-axis drives, butwith a more limited range of motion along the X-axis than the standardhead, may be utilized where the minimum gap between discs is less thanthat which will accommodate a standard head. The use of an inspectionhead having precisely controlled positioning means ensures that theinspection head may be located accurately and repeatably whereinspections are desired. For example, if an indication was found in aspecific location in a prior inspection, but the indication was notsufficient to take the disc out of service, the inspection head may beaccurately directed to the location where the indication appeared duringa subsequent inspection.

Accordingly, it is an object of the present invention to provide aninspection head capable of accurately and repeatably positioning anon-destructive inspection probe against a component to be inspected.

It is another object of the invention to provide an inspection headhaving independently and precisely controlled drive systems for eachaxis of movement.

It is a further object of the invention to provide an inspection headthat includes or omits specific drive mechanisms and specificdirections, permitting construction of an inspection head that may fitwithin a narrow space in a desired location, while still providing thenecessary range of motion to complete an inspection.

It is another object of the invention to provide an inspection head thatmay be utilized with one or two inspection probes.

It is a further object of the invention to provide an inspection headwhose range of motion and precise control of positioning enable bothstraight on and angled directional inspections, thereby permitting anindication detected by a straight on inspection to be more preciselylocated using the angled inspection.

It is a further object of the invention to provide an inspection headthat may be precisely positioned so that indications may be preciselylocated during pitch catch ultrasonic inspections.

It is a further object of the invention to provide an inspection headthat may be used interchangeably with a wide variety of non-destructiveinspection probes, for example, single ultrasonic, double ultrasonic,phased array ultrasonic, or eddy currents.

These and other objects of the invention will become more apparentthrough the following description and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an isometric back view of a standard inspection head accordingto the present invention, illustrating two inspection probes thereon.

FIG. 2 is an isometric back view of a standard inspection head accordingto the present invention, illustrating a single inspection probetherein.

FIG. 3 is an isometric, partially exploded back view of the upperportion of an inspection head according to FIG. 2.

FIG. 4 is an isometric, partially exploded back view of an inspectionprobe assembly according to the present invention.

FIG. 5 is an isometric, partially exploded back view of an X-axis drivemechanism for use with the inspection head of FIG. 2.

FIG. 6 is a partially exploded, isometric back view of a Y-axis drivemechanism for use with an inspection head of FIG. 2.

FIG. 7 is an isometric, back view of a low clearance inspection headaccording to the present invention.

FIG. 8 is an isometric, partially exploded back view of an upper portionof a low clearance inspection head according to FIG. 7.

FIG. 9 is an isometric back view of an inspection probe utilized withthe inspection head of FIG. 7.

FIG. 10 is an isometric, partially exploded back view of upper portionof an arc drive inspection head according to the present invention.

FIG. 11 is an isometric view of a pair of linear drive inspection headsaccording to the present invention.

FIG. 12 is an isometric, partially exploded back view of an upperportion of a linear drive inspection head according to the presentinvention.

FIG. 13 is a back view of an inspection head and inspection head liftingmechanism according to the present invention.

FIG. 14 is an environmental, isometric side view of an inspection headaccording to the present invention being utilized to perform aninspection on the discs of a fully assembled steam turbine rotor.

FIG. 15 is a back view of an inspection head and inspection head liftmechanism according to the present invention, being utilized to performan inspection.

FIG. 16 is a side view of a pair of arc drive inspection headsperforming an inspection on a disc of a steam turbine rotor assembly.

FIG. 17 is an isometric view of a pair of linear drive inspection headsaccording to the present invention as configured to perform aninspection on both sides of a disk simultaneously.

Like reference characters denote like elements throughout the drawings.

DETAILED DESCRIPTION

The present invention provides an inspection head for deliveringnon-destructive inspection probes to locations having limited spaces forsuch probes, for example, between adjacent discs of a turbine rotorassembly for inspection of the surfaces of those discs.

Referring to FIGS. 1-6, the first embodiment of the inspection head isillustrated, hereinafter called a standard head 10. Referring to FIGS.1-2, the standard head 10 includes a base 12 (partially shown)structured for mounting on a presently available apparatus for raisingthe inspection head between adjacent discs. Although such devices arepresently available, they will be briefly described below. A stand 14extends upward from the base 12. The stand 14 terminates in a railsupport plate 16. The rail support plate 16 supports a pair of rails 18on either side of a drive screw 20, with an endcap 22 on either end ofthe assembly. The drive screw 20 is rotably secured between the endcaps22, with an X-axis drive mechanism 24, which will be described ingreater detail below, operatively connected to one end of the drivescrew 20.

The stand 14 further includes a Y-axis drive mechanism 26, including afixed vertical rail 28 having a bracket 30 secured at its top end. Apair of sliders 32 are slidably mounted on the rail 28, with an arm 34extending upward from each slider 32 to the rail support plate 16. Inaddition to the movement of the rail support plate 16 with respect tothe base 12, the individual probe assemblies 36 may move vertically withrespect to the rail support plate 16. A motor driven screw rail 38, theoperation of which will be described below, provides for verticalpositioning adjustment of each probe assembly 36.

The standard head 10 is illustrated in more detail in FIGS. 3-6.Referring specifically to FIGS. 2 and 5, the drive screw 20 iscontrolled by the X-axis drive motor 40. The X-axis drive motor 40 ismounted to a motor mount 42 which is secured below one of the two endcaps 22. The motor 40 is connected through the bushing 44 to the pulley46, which drives the drive belt 48, thereby turning the pulley 50. Thepulley 50 is connected to the drive screw 20 through the thrust bearings52 and ball bearings 54, thereby facilitating rotation within the hole56 defined within the end cap 22.

Referring to FIGS. 2 and 6, the Y-axis drive mechanism 26 is illustratedin more detail. The Y-axis motor 58 is secured to the motor mount 60.The Y-axis motor 58 is operatively connected to the Y-axis drive screw38 through the thrust bearing 62, miter gear 64, miter gear 66, andthrust bearing 68, with the interaction of the two miter gears 64, 66inverting the horizontal rotation imparted by the motor 58 to thevertical rotation necessary to rotate the drive screw 38.

Referring to FIGS. 2-4, a probe assembly 36 is illustrated. The bottomof the probe assembly 36 includes a trolley plate 70, which isthreadedly engaged by the Y-axis drive screw 38 passing through theaperture 72 defined within the trolley plate 70. The screw rail end 74is located directly above the aperture 72. A pair of trolleys 76 aresecured to the lower side of the trolley plate 70, and are structured toengage the rails 18, thereby permitting the probe assembly 36 to slidealong the rails 18. A pair of pillow block assemblies 78 are disposed oneither side of the trolley plate 70, and define holes 80 therethrough,with the holes 80 being structured to receive a guide shaft 82 on eitherside of the Y-axis drive screw 38. This portion of the probe assembly 36remains adjacent to the rails 18, with the remainder of the probeassembly 36, described below, being structured for movement along theY-axis as controlled by the motor 58.

A shaft hangar 84 forms the lower portion of the movable part of theprobe assembly 36. Each end 86 of the shaft hangar 84 is structured toclamp around the guide shaft 82. A bracket 88 is disposed above theshaft hangar 84 motor mounts 90, 92 extend downward from the bracket 88and upward from the shaft hangar 84, respectively, and secure a Z-axismotor 94 therein. The Z-axis motor 94 turns the pulley 96, Which isoperatively connected to the Z-drive arm 98 that is partially securedabove the bracket 88. The bracket 88 further defines a pair of upwardextending end flanges 100, with a mount 102 centered thereon, and aplurality of roller slides 104 between each side of the mount 102 andthe corresponding flange 100. An alignment plate 106 is pivotallymounted to each side of the mount 102, and pivotally and slidablymounted across the roller slides 104 on that side and the upwardextending flange 100 of the bracket 88. Actuation of the Z-axis motor 94thereby causes the Z-drive arm 98 to move the mount 102 along theZ-axis, with the roller slides 104 ensuring that the movement impartedby the Z-axis motor 94 remains substantially along the Z-axis. Movementof the mount 102 in the opposite direction is achieved by springpressure on the Z-drive arm 98.

A U-shaped bracket 108 is pivotally mounted on the mount 102, with theends of the U-shape extending upward. The upper ends of the U-shapedefine a pair of holes 110, structured to receive a screw 112 passingthrough a thrust bearing 114 and ball bearing 116, into either side of aprobe plate 118, thereby pivotally securing the probe plate 118 withinthe bracket 108. A Θ-axis motor 120 is secured to the back of the probeplate 118 by the brackets 122 and clamps 124. The Θ-axis motor 120 isoperatively connected to the pulley 126, which is operatively connectedto the pulley 128 through the belt 130. The pulley 128 is in turnconnected to the worm gear shaft 132, mounted on the front of the probeplate 118, via the bearing 134. The worm gear shaft 132 engages the wormgear 136, to which the sensor 138 has been secured. The sensor 138 maybe an ultrasound sensor, eddy current sensor, or other non-destructiveinspection sensor. The sensor 138 may thereby be rotated around theΘ-axis by the Θ-axis motor 120 to change the angle at which a disc isinspected.

Referring to FIGS. 7-9, a low clearance head 140 is illustrated. The lowclearance head 140 is similar to the standard head 10 in many respects.The low clearance head 140 includes the base 142 structured for mountingon a presently available apparatus for raising the inspection headbetween adjacent discs. A stand 144 extends upward from the base 142.The stand 144 includes a fixed vertical rail 146 having a bracket 148secured at its top end. A pair of sliders 150 are slidably mounted onthe rail 144, with an arm 152 extending upward from each slider 150 toeither side of a top plate 154. A pair of arms 156 extends outward fromthe top plate 154, and may include rollers 158 pivotally secured totheir ends. A second pair of arms 160 extends outward from the arms 156,and include a pair of rollers 162 pivotally secured to their ends.

A Y-base plate 164 may be disposed on top of the top plate 154. A pairof bolsters 166 are disposed atop either side of the Y-base plate 164,with a thrust bearing 168 located between the top bolsters, on top ofthe Y-base plate. A Y-axis drive screw 170 extends upward through theY-base plate 164 and thrust bearing 168, terminating at its lower endwith the end cap 172. A pair of guide rods 174 are disposed on eitherside of the Y-axis drive screw 170, passing through the Y-base plate 164and top bolsters 166. The above described portion of the low clearancehead 140 remains stationary during movement in the Y-direction, whilethe following portion will move along the Y-axis.

A Y-drive base 176 is disposed at the top end of the guide rods 174 andY-axis drive screw 170. A support block 178 may be disposed below theY-drive base, surrounding and providing additional support for each ofthe guide rods 174. An endcap 180 surrounds and provides additionalsupport for the Y-axis drive screw 170. A Y-axis motor 182 is mounted ontop of the Y-drive base 176, and may be secured there by the motorbracket 184. The Y-axis motor 182 is operatively connected to the drivescrew 170 through the interaction of the miter gear 186, connected tothe Y-axis motor 182, and the miter gear 188, connected to the Y-axisdrive screw 170.

An X-axis motor 183 is mounted on a mounting plate 185, at the top ofthe guide rods 174. A dovetail slide 187 is mounted on the mountingplate 185, being operatively connected to the X-axis motor 183 by theinteraction of the miter gear 189, attached to the motor 183, and themiter gear 191, attached to the leadscrew 193 of the dovetail slide 187.The slider 195, threadedly connected to the leadscrew 193, is connectedto the Z-drive base 190.

A Z-drive base 190 is disposed above the Y-drive base 176, and supportsa Z-drive motor 192 thereon. The motor 192 is operatively connected to apulley 194. A slide mount plate 196 is disposed above the Z-drive base190 and Z-drive motor 192. The slide mount plate 196 defines a pair ofupwardly extending flanges 198 at each end. The head mount plate 104 iscentered on the slide mount plate 196, with a plurality of roller slides202 located between each side of the head mount plate 200 and thecorresponding upward flange 198. The roller slides 202 are allinterconnected to the directly adjacent roller slides 202, in a mannerthat permits only linear sliding motions in a Z direction with respectto each other. A Z-drive arm 204 is pivotally secured to the top surfaceof the slide mount plate 196, and is operatively connected to the pulley194 and the head mount plate 200. Actuation of the Z-axis motor 182thereby moves the pulley 194, thereby causing the Z-drive arm 204 tomove the head mount plate 200 along the Z-axis, with the roller slides202 limiting the movement of the head mount plate 200 to within theZ-axis. A probe assembly 36, identical to the probe assembly 36described above, is mounted on top of the head mount plate 200.

Referring to FIG. 10, an arc drive head 206 is illustrated. The arcdrive head 206 sits atop a base plate 208, which is similar to the topplate 154, and which may be used to attach the arc drive head 206 to abase 12 and stand 14, similar to those used for other inspection heads.The base plate 208 has an X-axis motor 210 secured thereto by the motorbracket portions 212, 214. The motor 210 turns a drive screw 216 mountedbetween a pair of end blocks 218, 220. A slider 222 is threadablysecured to the drive screw 216, and is rigidly attached to a slide base224. A pair of curved support arms 226, 228 extend upward from the slidebase 224, pivotally securing a probe frame 230 between their top ends. Aprobe 232 is secured within the probe frame 230 by a plurality of screws234 passing through the back 236 of the probe frame 230, and thenthreadably engaging the probe 232. Each of the screws 232 has a springdisposed thereon, thereby biasing the probe 232 away from the back 236of the probe frame 230. Rotation of the probe frame 230 about the Φ-axisis controlled by the Φ-axis motor 240, which is mounted on the probesupport arm 226 by the motor bracket 242. The motor 240 is operativelyconnected to a worm gearshaft 244, extending upward therefrom, and whichengages the worm gear 246 mounted on the side 248 of the probe housing230.

Referring to FIGS. 11-12, a linear drive head 250 is illustrated. Thelinear drive head 250 includes a base plate 252 that is similar to thebase plate 208. An X-axis drive motor 254 is secured to the base platebetween the brackets 256, 258. The motor 254 is operatively connected toa drive screw 260 housed within a slide 262, mounted on the base plate252. A pulley 262 connected to the motor 254 is connected by a belt to apulley 264 connected to the X-axis drive screw 260. A slide base 266 isthreadably secured to the X-axis drive screw 260, so that the movementof the slide base 266 and the X-axis direction is controlled by themotor 254.

A pair of generally L-shaped arms 268 are secured to the slide base 266,and a slider 276 is secured between the L-shaped arms 268, with thebracket 278 therebetween. The bracket 278 is biased away from the slidebase 266 by the spring 270. A cable 272 secured at one end to a bracket274 which is itself secured to the bracket 278 may be used to pull thebracket 278 towards the slide base 266. A Y-axis drive screw 280 issecured within the slider 276, and has a pulley 282 at one end. A Y-axismotor 284 is secured to the top of the slider 276 by the bracket 286,and is operatively connected to the pulley 288. A belt between thepulleys 282, 288 thereby permits the Y-axis motor 284 to control theY-axis drive screw 280. An outer probe frame 290 is threadably securedto the Y-axis drive screw 280. An inner probe frame 292 is securedwithin the outer probe frame 290 by a plurality of screws 294, each ofwhich has a spring 296 disposed thereon between the outer probe frame290 and inner probe frame 292, thereby biasing the inner probe frame 292away from the outer probe frame 290. A probe 298 is housed within theinner probe frame 292. As with all other inspection heads, on the probe298 may be an ultrasonic inspection probe, an eddy current inspectionprobe, or other non-destructive inspection probe. A pair of rollers 300are disposed near the top of the linear drive head 250, and in theillustrated embodiment are secured to the arm 302 secured to the bracket286.

Referring to FIGS. 13-15, a probe insertion apparatus 304 isillustrated. The probe insertion apparatus 304 includes a base 306having a stationary telescoping member 308 extending upward therefrom. Asliding telescoping member 310 fits around the stationary telescopingmember 308. Any of several inspection heads may be secured to the top ofthe sliding telescoping member 310. The sliding telescoping member maybe caused to move up and down with respect to the stationary telescopingmember using any of several means that are well known in the art, forexample, manually, through the use of hydraulic cylinders, through theuse of an electric motor driving an appropriate pulley and/or gearsystem, etc. Because such systems are well known in the prior art, theywill not be described further herein. When an inspection is desired, thesliding telescoping member may be raised with respect to the stationarytelescoping member from the position of FIG. 13 to the position of FIGS.14-15, thereby locating the appropriate inspection head between a pairof turbine discs 312, 314. The inspection head may then be moved intoengagement with the disc as described above. In the case of the lineardrive head of FIGS. 11-12, the spring 270 is allowed to bias the arms268 to rotate the inspection head 250 against the disc 316. In the caseof the arc drive head of FIGS. 10 and 16, the Θ-axis motor 240 will beactuated to orient the probe 232 along the surface of the disc 318. Inthe case of the low clearance head of FIG. 15, the inspection head 140will be moved along the X, Y, and Z-axes until it properly engages thedisc 318. Depending upon the inspection to be performed, the disc may berotated while the inspection head remains stationary, or the disc mayremain stationary while the inspection head is moved along one of itsaxes of movements.

As another alternative, the standard head may be configured to place twoprobes on the same side or opposite sides of the disc. FIG. 1illustrates a pair of inspection heads 36, each of which may moveindependently of the other along the X, Z, and/or Θ axis. As a furtheralternative, any head may be used in pairs, on opposite sides of a disc,either for pitch-catch inspection or merely to reduce the time requiredto perform an inspection as shown by the pair of linear drive heads 250in FIG. 17. Each linear drive head 250 is supported by a stand 318connected to a common base 320, so that both heads 250 may be placedadjacent to opposite sides of a disk simultaneously. In a pitch-catchinspection, which is well-known in the art of nondestructive testing,one probe transmits an ultrasonic signal that is received by the otherprobe.

The present invention therefore provides an inspection head capable ofaccurately and repeatably positioning a non-destructive inspection probeagainst a component to be inspected. The inspection head hasindependently and precisely controlled drive systems for each axis ofmovement, and is constructed in a manner that permits the inspectionhead to fit within relatively inaccessible locations. The inspectionhead may be utilized with either ultrasound, eddy current, or othernon-destructive inspection probes, may be utilized with individual ormultiple probes, and enables both straight and angled directionalinspections.

While specific embodiments of the invention have been described indetail, it will be appreciated by those skilled in the art that variousmodifications and alternatives to those details could be developed inlight of the overall teachings of the disclosure. Accordingly, theparticular arrangements disclosed are meant to be illustrative only andnot limiting as to the scope of the invention which is to be given thefull breadth of the appended claims and any and all equivalents thereof.

1. A nondestructive inspection head, comprising: means for raising and lowering the head into a location to be inspected; an X-axis drive; a drive selected from the group consisting of a Y-axis drive and a Φ-axis drive; and a sensor.
 2. The inspection head according to claim 1, further comprising a Z-axis drive.
 3. The inspection head according to claim 2, wherein the Z-axis drive includes a motor structured to drive the head in a first direction, and a spring structured to drive the head in an opposing direction.
 4. The inspection head according to claim 3, further comprising: a plurality of interconnected, substantially parallel slides adjacent to each other and structured to slide with respect to each other; an arm structured to actuate sliding motion of the sliders; a spring structured to bias the arm in a first direction; and a motor-driven pulley structured to move the arm in the opposing direction.
 5. The inspection head according to claim 1, further comprising a θ-axis drive.
 6. The inspection head according to claim 5, wherein the θ-axis drive includes a motor-driven belt, with the belt driving a leadscrew operatively connected to a gear that is operatively connected to the head.
 7. The inspection head according to claim 1, wherein the X-axis drive includes a lead screw actuated by a motor-driven pulley.
 8. The inspection head according to claim 1, further comprising a probe holder structured to hold a probe in a floating manner.
 9. The inspection head according to claim 1, wherein the probe is selected from the group consisting of ultrasound and eddy current.
 10. The inspection head according to claim 9, further comprising a pair of ultrasonic probes.
 11. The inspection head according to claim 9, further comprising a means for dispensing a coupling media around an ultrasonic sensor.
 12. The inspection head according to claim 11: wherein the coupling media is water; and further comprising a catch basin and holding tank structured for recycling the water.
 13. The inspection head according to claim 1, further comprising at least two rollers structured to engage a surface of a component being inspected.
 14. The inspection head according to claim 1, wherein the probe is secured within a probe housing, and the probe is spring-biased away from the probe housing. 